1. Field of the Invention
The present invention generally relates to a method and an apparatus for controlling an audio output, and more particularly, to a method for automatically controlling an output volume of audio suited to the impedance of a head phone when the head phone is connected to a portable terminal.
2. Description of the Related Art
In recent years, with the significant development of information and communication technology and a semiconductor technology, supply and use of all types of mobile terminals have rapidly increased. In particular, mobile terminals have developed to a mobile convergence stage including traditional functions and other unique terminal functions.
For example, in recent years, portable terminals have provided a multi-media function such as a TV viewing function (e.g., mobile broadcasting such as DMB (Digital Multimedia Broadcasting) or DVB (Digital Video Broadcasting)) as well as general communication functions such as voice call or message transmission/reception.
Portable terminals may also be connected to head phones, such as an ear piece or ear phones through an interface unit such as an ear jack, and may output an audio signal to the head phones through the interface unit. The head phones convert the audio signal into an output sound. Herein, the head phones may be interchangeably described as head phones, a head phone, a head phone set, and the like.
A volume of the sound output from the head phones may vary according to manufacturer, model, and product specification of the head phones. Upon purchasing the portable terminal, the user may receive bundle head phones. The term “bundle” refers to a product sold as a package. For example, the portable terminal may be sold together with a charger, a protection film, and software, as well as the head phones.
An amplitude of a sound output from the portable terminal may be set corresponding to impedance of bundle headphones. Accordingly, when the user uses other head phones (that is, head phones having impedance different from that of the bundle head phones), the amplitude of the sound may be larger or smaller than expected. For example, when head phones having impedance of 300Ω are connected to a portable terminal set corresponding to 30Ω, the amplitude of the sound output through the connected head phones may be too small. In an opposite case, the amplitude of the sound output through the connected head phones may be large.
A control technology of audio output for minimizing the above phenomenon has been developed. That is, the control technology according to the related art detects impedance of connected head phones and controls amplification gain of an audio signal based on the detected impedance to provide stable sound to the user when the head phones are connected to the portable terminal.
However, the control technology of the related art does not consider motional impedance generated when a vibration plate of the head phones vibrates due to neighboring noise. That is, impedance of the head phones detected by the portable terminal is changed according to the neighboring noise; accordingly, the volume of the sound may not be stable.